Interpretive Summary: Phenolic compounds (flavonoids, polymeric flavonoids, and phenolic acids) have been suggested to have health-promoting benefits. Careful evaluation of their health potential requires analytical methods for their identification and quantification in foods. This is a daunting task since there are believed to be more than 5,000 glycosylated flavonoids (flavonoids with one or more sugars attached) in commonly consumed foods. This paper describes a screening method that uses a standard analytical approach (i.e. the same extraction, separation, and detection method) to initially analyze all samples and standards. Data from this screening method can be used to provide identification of specific compounds using standards and published literature. Without standards or literature values, the method still provides provisional identification of the compounds---that is identification of subgroups (flavonoid, sugar, and organic acid) but not linkage sites between the sub-groups.

Technical Abstract:
A screening method was developed for the systematic identification of glycosylated flavonoids and other phenolic compounds in plant food materials based on an initial, standard analytical method. This approach applies the same analytical scheme (aqueous methanol extraction, reverse phase liquid chromatographic separation, and diode array and mass spectrometric detection) to every sample and standard. This standard approach allows the cross comparison of compounds in samples, standards, and plant materials previously identified in the published literature. Thus, every analysis contributes to a growing library of data for retention times and molecular and mass spectra. Without authentic standards, this method provides provisional identification of the phenolic compounds; identification of flavonoid backbones, phenolic acids, saccharides, and alkyls, but not the positions of the linkages between these subgroups. With standards, this method provides positive identification of the full compound; identification of subgroups and linkages. The utility of the screening method is demonstrated in this study by the identification of 78 phenolic compounds in cranberry, elder flower, Fuji apple peel, navel orange peel, and soybean seed.